Flexible display panel and manufacturing method thereof

ABSTRACT

A flexible display panel and a manufacturing method which is capable of removing a non-display area without damaging a display element layer, the flexible display panel includes a flexible substrate which includes a display area and a peripheral area outside of the display area, a display element layer disposed on the flexible substrate, and a neutral plane balancing layer disposed on the display element layer in the peripheral area, wherein the peripheral area of the flexible substrate in which the neutral plane balancing layer is disposed is folded towards a rear side of the display area along a first bending line, and the neutral plane balancing layer overlaps the first bending line.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/661,823, filed Oct. 23, 2019, which is a continuation of U.S. patentapplication Ser. No. 15/871,072, filed Jan. 15, 2018, now U.S. Pat. No.10,461,267, which is a continuation of U.S. patent application Ser. No.14/256,581, filed Apr. 18, 2014, now U.S. Pat. No. 9,882,152, whichclaims priority to and the benefit of Korean Patent Application No.10-2013-0122078, filed Oct. 14, 2013, the entire content of all of whichis incorporated herein by reference.

BACKGROUND 1. Field

The present invention relates to a flexible display panel and amanufacturing method thereof. More particularly, the present inventionrelates to a flexible display panel and a manufacturing method thereofwhich are capable of removing a non-display area without damaging adisplay element layer.

2. Description of the Related Art

A display device such as a liquid crystal display (LCD), an organiclight emitting diode (OLED) display, and an electrophoretic displayinclude a field generating electrode and an electro-optical activelayer.

For example, the organic light emitting diode (OLED) display includes anorganic light emitting layer as the electro-optical active layer.

The field generating electrode is connected to a switching element suchas a thin film transistor to receive a data signal, and theelectro-optical active layer converts the data signal to an opticalsignal to display an image.

Among the display devices, since the organic light emitting diode (OLED)display, as a self-light emitting type, does not require an additionallight source, it is advantageous in terms of power consumption, responsespeed and, viewing angle, and contrast ratio are excellent.

The organic light emitting diode (OLED) display includes a plurality ofpixels such as red pixels, blue pixels, green pixels, and white pixels,and may express full colors by combining the pixels.

Each pixel includes an organic light emitting element, and a pluralityof thin film transistors for driving the organic light emitting element.

The light emitting element of the organic light emitting diode (OLED)display includes a pixel electrode, a common electrode, and a lightemitting layer interposed between the two electrodes.

One of the pixel electrode and the common electrode becomes an anode,and the other becomes a cathode.

An electron injected from the cathode and a hole injected from the anodeare coupled with each other in the light emitting layer to form anexciton, and the exciton emits light while discharging energy.

The common electrode is formed throughout a plurality of pixels, andtransfers a predetermined common voltage.

In the case of the organic light emitting diode (OLED) display, toreduce reflection of external light, a polarizing plate may be attachedto an upper part of a display panel, a touch panel may be attached tothe upper part of the display panel to sense external contact, or alower passivation film may be attached to a bottom side of the displaypanel.

In cases where the display panel of the display device uses a glasssubstrate which is heavy and easily damaged, there is a limitation inits portability and implementation of a large-scale screen display.

Thus, recently, a display device which is light, strong against impact,and uses a flexible plastic substrate has been developed.

Meanwhile, the display panel of the display device includes a displayarea where a plurality of display pixels are disposed, and a peripheralarea surrounding the display area.

The peripheral area is provided with various kinds of wires fortransmitting a driving signal to a signal line connected to a thin filmtransistor of the display area, and various kinds of voltage pads forreceiving voltages from an external source.

The peripheral area forms a non-display area because it does not displayan image, and the display area is reduced as the non-display areaincreases.

Recently, demand for a display device having a smaller non-display areais increasing.

The above information disclosed in this Background section is only forenhancement of an understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known to a person of ordinary skill in the art.

SUMMARY

In embodiments of a flexible display device, when a display panel is tobe folded in order to remove a non-display area, a large amount ofstress is applied to a layer of the display panel where a thin filmtransistor and a light emitting element are disposed, thereby damagingthe display panel.

When the thin film transistor and the light emitting element aredamaged, these elements do not properly function or the performancethereof may be deteriorated to cause problems in display quality of animage, and stress due to bending may be accumulated to cause cracks ordelamination of the display element layer.

Embodiments of the present invention have been made in an effort toprovide a flexible display panel and a manufacturing method thereofwhich is capable of removing a non-display area without damaging adisplay element layer which includes a thin film transistor and a lightemitting element.

A flexible display panel according to an exemplary embodiment of thepresent invention includes a flexible substrate including a display areaand a peripheral area outside of the display area, a display elementlayer disposed on the flexible substrate, and a neutral plane balancinglayer disposed on the display element layer in the peripheral area,wherein the peripheral area of the flexible substrate in which theneutral plane balancing layer is disposed is folded towards a rear sideof the display area along a first bending line, and the neutral planebalancing layer overlaps the first bending line.

A lower passivation film may be disposed under the flexible substrate,and a bottom side of the lower passivation film may include a pluralityof grooves.

A thickness of the neutral plane balancing layer may be from about 10 μmto about 150 μm.

The neutral plane balancing layer may include an acryl or silicon-basedresin.

The neutral plane balancing layer may further include nanoparticles ormicro-particles.

The curvature radius of the flexible substrate folded along the firstbending line may be from about 0.5 mm to about 10 mm.

The display element layer may include a plurality of thin filmtransistors, a plurality of light emitting elements, and anencapsulation layer sealing the light emitting elements.

The peripheral area includes a first peripheral area in which a wiringportion is disposed and a second peripheral area in which a pad area isdisposed, and the neutral plane balancing layer may be formed in thesecond peripheral area.

A flexible display panel according to another exemplary embodiment ofthe present invention includes a flexible substrate including a displayarea and a peripheral area outside of the display area, a displayelement layer disposed on the flexible substrate, and a lowerpassivation film disposed under the flexible substrate, wherein a bottomside of the lower passivation film includes a plurality of grooves, andthe peripheral area of the flexible substrate is folded towards a rearside of the display area along a first bending line.

A neutral plane balancing layer may be disposed on the display elementlayer of the peripheral area.

The neutral plane balancing layer may overlap the first bending line.

A part of the peripheral area folded towards the rear side of thedisplay area may be folded outwards along a second bending line disposedoutside of the first bending line.

A flexible display panel according to another exemplary embodiment ofthe present invention includes a flexible substrate which includes adisplay area and a peripheral area outside of the display area, and adisplay element layer disposed on the flexible substrate, wherein aperipheral area of the flexible substrate is folded towards a rear sideof the display panel along a first bending line, and a part of theperipheral area folded towards the rear side of the display area isfolded outwards along a second bending line which is disposed outside ofthe first bending line.

A lower passivation film may be disposed under the flexible substrate,and a bottom side of the lower passivation film may include a pluralityof grooves.

A manufacturing method of a flexible display panel according to anexemplary embodiment of the present invention includes forming a displayelement layer by laminating a plurality of thin films on a flexiblesubstrate which includes a display area and a peripheral area outside ofthe display area, forming a neutral plane balancing layer on the displayelement layer in the peripheral area, and folding the peripheral area ofthe flexible substrate where the neutral plane balancing layer isdisposed towards a rear side of the display panel along a first bendingline, and wherein the neutral plane balancing layer overlaps the firstbending line.

The method further includes attaching a lower passivation film to abottom side of the flexible substrate, and a bottom side of the lowerpassivation film may include a plurality of grooves.

A manufacturing method of a flexible display panel according to anotherexemplary embodiment of the present invention includes forming a displayelement layer on a flexible substrate which includes a display area anda peripheral area outside of the display area, attaching a lowerpassivation film to a bottom side of the flexible substrate, and bendingthe peripheral area of the flexible substrate towards a rear side of thedisplay area along a first bending line, wherein a bottom side of thelower passivation film includes a plurality of grooves.

The method further includes forming a neutral plane balancing layer onthe display element layer in the peripheral area.

The method may further includes folding a part of the peripheral areaforward along a second bending line disposed outside of the firstbending line before folding the peripheral area of the flexiblesubstrate towards the rear side of the display area along the firstbending line.

A manufacturing method of a flexible display panel according to anotherexemplary embodiment of the present invention includes forming a displayelement layer on a flexible substrate which includes a display area anda peripheral area outside of the display area, folding a part of theperipheral area forward along a first bending line crossing theperipheral area, and folding the folded peripheral area towards the rearside of the display area along a second bending line disposed inside ofthe first bending line.

According to an exemplary embodiment of the present invention, anon-display area may be removed without damaging a display element layerwhich includes a thin film transistor and a light emitting element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a display panel before a peripheral area isfolded backwards in a manufacturing process of a flexible display panelaccording to an exemplary embodiment of the invention.

FIG. 2 is a layout view showing a pixel of the display panel accordingto an exemplary embodiment of the present invention.

FIG. 3 is a cross-sectional view of the display panel of FIG. 2 takenalong the line III-III.

FIG. 4A, FIG. 4B, and FIG. 4C are top plan views of the display panelbefore the peripheral area is folded backwards in a manufacturingprocess of a flexible display panel according to an exemplary embodimentof the present invention.

FIG. 5A and FIG. 5B are cross-sectional views of the display panel ofFIG. 4A taken along the line V-V.

FIG. 6 is a cross-sectional view of a lower passivation film of thedisplay panel according to an exemplary embodiment of the presentinvention.

FIG. 7 is a cross-sectional view showing a state in which the peripheralarea of the display panel according to an exemplary embodiment of thepresent invention is folded backwards.

FIG. 8 is a top plan view showing a state in which the peripheral areaof the display panel according to an exemplary embodiment of the presentinvention is folded backwards.

FIG. 9 is a cross-sectional view showing a state in which the peripheralarea of the display panel according to an exemplary embodiment of thepresent invention is folded backwards.

FIG. 10 is a top plan view of the display panel before the peripheralarea is folded backwards in a manufacturing process of a flexibledisplay panel according to an exemplary embodiment of the invention.

FIG. 11 is a cross-sectional view of the display panel of FIG. 10 takenalong the line XI-XI.

FIG. 12 is a cross-sectional view showing a state in which a part of theperipheral area of the display panel according to an exemplaryembodiment of the present invention is folded forwards.

FIG. 13 is a cross-sectional view showing a state in which a part of thedisplay panel of FIG. 12 is folded backwards.

FIG. 14 is a cross-sectional view showing a state in which a part of theperipheral area of the display panel according to an exemplaryembodiment of the present invention is folded forwards.

FIG. 15 is a cross-sectional view showing a state in which a part of thedisplay panel of FIG. 14 is folded backwards.

DETAILED DESCRIPTION

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown.

As those skilled in the art would realize, the described embodiments maybe modified in various different ways, all without departing from thespirit or scope of the present invention.

In the drawings, the thickness of layers, films, panels, regions, etc.,are exaggerated for clarity.

Like reference numerals designate like elements throughout thespecification.

It will be understood that when an element such as a layer, film,region, or substrate is referred to as being “on” another element, itcan be directly on the other element or intervening elements may also bepresent.

In contrast, when an element is referred to as being “directly on”another element, there are no intervening elements present.

First, Referring to FIG. 1 through FIG. 8, a flexible display panel andits manufacturing method according to an exemplary embodiment of thepresent invention will be described. FIG. 1 is a top plan view of adisplay panel before a peripheral area is folded backwards in amanufacturing process of a flexible display panel according to anexemplary embodiment of the invention, FIG. 2 is a layout view showing apixel of the display panel according to an exemplary embodiment of thepresent invention, FIG. 3 is a cross-sectional view of the display panelof FIG. 2 taken along the line III-III, FIG. 4A, FIG. 4B, and FIG. 4Care top plan views of the display panel before the peripheral area isfolded backwards in a manufacturing process of a flexible display panelaccording to an exemplary embodiment of the present invention, FIG. 5Aand FIG. 5B are cross-sectional views of the display panel of FIG. 4Ataken along the line V-V, FIG. 6 is a cross-sectional view of a lowerpassivation film of the display panel according to an exemplaryembodiment of the present invention, FIG. 7 is a cross-sectional viewshowing a state in which the peripheral area of the display panelaccording to an exemplary embodiment of the present invention is foldedbackwards, and FIG. 8 is a top plan view showing a state in which theperipheral area of the display panel according to an exemplaryembodiment of the present invention is folded backwards.

First, referring to FIG. 1 through FIG. 3, a flexible substrate 112 isformed on a supporting substrate (not shown) made of glass or plastic.

When viewed on a plane, the flexible substrate 112 includes a displayarea DA for displaying an image and a peripheral area PA outside of thedisplay area.

The supporting substrate may be various kinds of substrates which arecapable of supporting the flexible substrate 112 and enduremanufacturing stresses.

The supporting substrate will be removed on completion of the flexibledisplay panel.

The flexible substrate 112 may include a flexible plastic.

For example, the flexible substrate 112 may include polyethyleneterephthalate (PET), polyethylene naphthalate, polycarbonate,polyarylate, polyetherimide, polyether sulfone, polyimide, and the like.

Next, a barrier layer 111 may be formed on the flexible substrate 112.

The barrier layer 111 may prevent external impurities from penetratingthrough the flexible substrate 112 and then permeating into a displayelement layer disposed thereon, and a surface of the barrier layer 111may be smooth.

The barrier layer 111 may include at least one of an organic orinorganic film. For example, the barrier layer 111 may include a siliconnitride (SiN_(x)), a silicon oxide (SiO_(x)), or a silicon oxynitride(SiO_(x)N_(y)).

The barrier layer 111 may be omitted.

Next, a display element layer 200 including a plurality of thin films isformed on the barrier layer 111.

The display element layer 200 includes a plurality of signal lines whichare disposed at the display area, and a plurality of pixels PX which areconnected to the signal lines and are arranged in an approximate matrixform.

The signal lines may include a plurality of scanning signal lines totransmit a scanning signal, and a plurality of data lines to transmit adata signal.

The display element layer 200 may include wiring portions WR1 and WR2which are disposed at the peripheral area PA, and a pad area PDA whichis connected to a driving portion (not illustrated) to drive pixels PX.

Accordingly, the peripheral area PA includes a first peripheral areaPA_a in which the wiring portions WR1 and WR2 are disposed, and a secondperipheral area PA_b in which the pad area PDA is disposed.

The pad area PDA and wiring portions WR1 and WR2 may be connected toeach other, and may be made of a conductive material.

The wiring portions WR1 and WR2 may be connected to a plurality ofsignal lines in the display area DA, and may be disposed at respectivelateral sides of the display area DA.

The driving portion may include a scan driver (not illustrated) totransmit scanning signals or a data driver (not illustrated) to transmitdata signals.

The driving portion may be directly mounted on the pad area PDA abovethe flexible substrate 112 in an IC chip form, or may be mounted on aflexible printed circuit film (not illustrated) or on a circuit board,and may be connected to the pad area PDA on the flexible substrate 112in a tape carrier package TCP form.

Now, referring to FIG. 2 and FIG. 3, a structural example of a displayelement layer 200 of the flexible display panel will be described.

A plurality of first and second semiconductors 154 a and 154 b areformed on the barrier layer 111.

The first semiconductor 154 a may include a channel region (notillustrated), a source region (not illustrated), and a drain region (notillustrated) which are disposed at respective lateral sides of thechannel region and are formed to be doped.

The second semiconductor 154 b may include a channel region 152 b, asource region 153 b and a drain region 155 b which are disposed atrespective lateral sides of the channel region 152 b and are formed tobe doped.

The first and second semiconductors 154 a and 154 b may includeamorphous silicon, polysilicon, or an oxide semiconductor.

A gate insulation layer 140 made of a silicon nitride (SiN_(x)) or asilicon oxide (SiO_(x)) is disposed on the first and secondsemiconductors 154 a and 154 b.

A plurality of scanning signal lines 121 including a first controlelectrode 124 a and a plurality of gate conductors including a secondcontrol electrode 124 b are formed on the gate insulation layer 140.

The scanning signal lines 121 transfer scanning signals, and may extendmainly in a horizontal direction.

The first control electrode 124 a may extend upwards from the scanningsignal lines 121.

The second control electrode 124 b is separated from the scanning signallines 121.

Though not illustrated, the second control electrode 124 b may include astorage electrode extending in a vertical direction.

The first control electrode 124 a may overlap a part of the firstsemiconductor 154 a, particularly the channel region, and the secondcontrol electrode 124 b may overlap a part of the second semiconductor154 b, particularly the channel region 152 b.

A first passivation layer 180 a is disposed on the gate insulation layer140 and the gate conductor.

The first passivation layer 180 a and the gate insulation layer 140include a contact hole 183 a which exposes the source region of thefirst semiconductor 154 a, a contact hole 185 a which exposes the drainregion, a contact hole 183 b which exposes the source region 153 b ofthe second semiconductor 154 b, and a contact hole 185 b which exposesthe drain region 155 b.

The first passivation layer 180 a includes a contact hole 184 whichexposes the second control electrode 124 b.

A plurality of data conductors including a plurality of data lines 171,a plurality of driving voltage lines 172, and a plurality of dataconductors which include a plurality of first output electrodes 175 aand a plurality of second output electrodes 175 b are formed on thefirst passivation layer 180 a.

The data lines 171 transmit data signals, and may mainly extend in avertical direction to cross the scanning signal lines 121.

Each data line 171 includes a plurality of first input electrodes 173 awhich extend toward the first control electrode 124 a.

The driving voltage lines 172 transfer a driving voltage, and may mainlyextend in a vertical direction to cross the scanning signal lines 121.

Each driving voltage line 172 includes a plurality of second inputelectrodes 173 b which extend toward the second control electrode 124 b.

In case the second control electrode 124 b includes the storageelectrode, the driving voltage lines 172 may include a part whichoverlaps the storage electrode.

The first and second output electrodes 175 a and 175 b are separatedfrom each other to have an island shape, and are separated from the datalines 171 and the driving voltage lines 172.

The first input electrode 173 a and the first output electrode 175 aface each other on the first semiconductor 154 a, and the second inputelectrode 173 b and the second output electrode 175 b equally face eachother on the second semiconductor 154 b.

The first input electrode 173 a and the first output electrode 175 a maybe respectively connected to the source region and the drain region ofthe first semiconductor 154 a through the contact holes 183 a and 185 a.The first output electrode 175 a may be connected to the second controlelectrode 124 b through the contact hole 184.

The second input electrode 173 b and the second output electrode 175 bmay be respectively connected to the source region 153 b and the drainregion 155 b of the second semiconductor 154 b through the contact holes183 b and 185 b.

The first control electrode 124 a, the first input electrode 173 a, andthe first output electrode 175 a form a switching thin film transistorQs together with the first semiconductor 154 a, and the second controlelectrode 124 b, the second input electrode 173 b, and the second outputelectrode 175 b form a driving thin film transistor Qd together with thesecond semiconductor 154 b.

However, the structure of the switching transistor Qs and the drivingtransistor Qd is not limited thereto, and may be variously modified.

A second passivation layer 180 b made of an inorganic insulator such asa silicon nitride or a silicon oxide may be disposed on the dataconductor.

The second passivation layer 180 b may have a smooth surface by removingsteps in order to improve light emission efficiency of the organic lightemitting element to be formed thereon.

The second passivation layer 180 b may include a contact hole 185 cwhich exposes the second output electrode 175 b.

A plurality of pixel electrodes 191 are formed on the second passivationlayer 180 b.

The pixel electrode 191 of each pixel PX is physically and electricallyconnected to the second output electrode 175 b through the contact hole185 c of the second passivation layer 180 b.

The pixel electrode 191 may include a semi-transmissive conductivematerial or a reflective conductive material

A pixel definition layer 360 (also referred to as a partition) having aplurality of openings exposing the pixel electrode 191 may be disposedon the second passivation layer 180 b.

The openings of the pixel definition layer 360 exposing the pixelelectrode 191 may define each pixel area.

The pixel definition layer 360 may be omitted.

A light emitting member 370 is positioned on the pixel definition layer360 and the pixel electrode 191.

The light emitting member 370 may include a first organic common layer371, a plurality of light emitting layers 373, and a second organiccommon layer 375 which are laminated in sequence.

The first organic common layer 371 may include, for example, at leastone of a hole injecting layer and a hole transport layer which arelaminated in sequence.

The first organic common layer 371 may be formed all over the displayarea in which the pixel PX is disposed, or may be formed only in eachpixel PX area.

The light emitting layer 373 may be disposed on the pixel electrode 191of each corresponding pixel PX.

The light emitting layer 373 may be made of an organic material whichuniquely emits light of the primary colors such as red, green, and blue,and may have a structure in which a plurality of organic material layersemitting light of different colors are laminated.

The second organic common layer 375 may include, for example, at leastone of an electron transport layer and an electron injecting layer whichare laminated in sequence.

The second organic common layer 375 may be formed all over the displayarea in which the pixel PX is disposed, or may be formed only in eachpixel PX area.

The first and second organic common layers 371 and 375 are provided toimprove light emitting efficiency of the light emitting layer 373, andone of the first and second organic common layers 371 and 375 may beomitted.

A common electrode 270 transmitting a common voltage Vss is formed onthe light emitting member 370.

The common electrode 270 may include a transparent conductive material.

For example, the common electrode 270 is made of a transparentconductive material, or may formed by thinly laminating metals such ascalcium (Ca), barium (Ba), magnesium (Mg), aluminum (Al), and silver(Ag) to have a light transmitting property.

The pixel electrode 191, the light emitting member 370, and the commonelectrode 270 of each pixel PX form a light emitting diode LD, and oneof the pixel electrode 191 and the common electrode 270 becomes acathode and the other becomes an anode.

Further, the storage electrode driving voltage lines 172 overlapped witheach other may form a storage capacitor Cst.

The display element layer 200 according to an exemplary embodiment ofthe present invention may employ a top emission method which displays animage by emitting internal light of the light emitting member 370towards a frontal direction of the flexible substrate 112.

An encapsulation layer 379 may be further formed on the common electrode270.

The encapsulation layer 379 may encapsulate the light emitting member370 and the common electrode 270 to prevent external moisture and oxygenfrom permeating.

A top surface of the encapsulation layer 379 may be smooth.

The encapsulation layer 379 may include a plurality of thin film layers.

For example, the encapsulation layer 379 may have a multi-layeredstructure including at least one of an organic film and an inorganicfilm.

Thus, the display element layer 200 including the thin film transistor,the light emitting diode LD, and the encapsulation layer 379 may becompleted.

The wiring portions WR1 and WR2 and the pad area PDA of the peripheralarea PA are disposed at the same layer as the gate conductive layer ordata conductive layer, and may be integrally formed when the gateconductive layer or data conductive layer is formed.

Referring to FIG. 4A to FIG. 5B, a neutral plane balancing layer 380 isformed in at least a part of the peripheral area PA.

The neutral plane balancing layer 380 is disposed above the displayelement layer 200.

The neutral plane balancing layer 380 may be formed to at least overlapa bending line CL of the second peripheral area PA_b along which theflexible display panel is later folded.

For example, the neutral plane balancing layer 380 may be formed, asshown in FIG. 4A, all over the second peripheral area PA_b in which thepad area PDA is disposed, or may be formed, as shown in FIG. 4B, tooverlap a bending line CL of the second peripheral area PA_b along whichthe flexible display panel is later folded, or may be formed, as shownin FIG. 4C, not only in the second peripheral area PA_b but also in atleast a part of the peripheral area.

The neutral plane balancing layer 380 moves up the position of theneutral plane NP in which strain is virtually zero when the peripheralarea PA is folded towards a rear side of the display area DA based onthe bending line CL, to dispose the neutral plane NL close to thedisplay element layer 200 or to allow a compressive stress, not atensile stress, to be applied to the display element layer 200.

Herein, the bending line CL may be a virtual border line between thedisplay area DA and the first peripheral area PA_a, or may be disposedon the periphery of the border line.

The thickness T1 of the neutral plane balancing layer may be from about10 μm to about 150 μm and an elastic coefficient may be from about 500MPa to about 100 GPa, but they are not limited thereto, and may bedependent on design specifications of the display panel such as thethickness of the display element layer 200 and the like.

The neutral plane balancing layer 380 may include an acryl or asilicon-based resin, or may include a resin having fine particles.

The fine particles may include rubber including silica, epoxy,polymer-based nanoparticles such as an epoxy hybrid and the like, ormicro-particles and the like.

In addition, the neutral plane balancing layer 380 may include variouskinds of films including polyethylene terephthalate (PET) and the like.

The horizontal width D1 of the first peripheral area PA_a may be widerthan that of the conventional peripheral area.

For example, the horizontal width D1 of the first peripheral area PA_amay be from about two to about six times larger than that of theconventional peripheral area.

For example, the horizontal width D1 of the first peripheral area PA_amay be wider than about 2 mm, but it is not limited thereto, and may beappropriately adjusted.

As such, if the horizontal width of the first peripheral area PA_a iswidened, when the first peripheral area PA_a is folded toward a rearside of the display area, bending may be performed only in the firstperipheral area PA_a, and the rigidity of the first peripheral area isdecreased such that the first peripheral area PA_a can be easily bent.

Referring to FIG. 5A or FIG. 5B, an anti-reflection layer 390, whichimproves visibility by reducing reflection of external light, may beattached to an upper part of the display element layer 200 of thedisplay area DA.

The anti-reflection layer 390 may be disposed only in the display areaDA, or may be disposed to be extended to the first peripheral area PA_atogether with the display area DA.

The anti-reflection layer 390 may include a polarizer (not illustrated)or a plurality of thin film layers (not illustrated).

In instances where the anti-reflection layer 390 includes a plurality ofthin film layers, the plurality of thin film layers may include at leastone thin metal film layer and at least one dielectric layer which arealternately laminated.

Next, the supporting substrate is separated from the flexible substrate112.

Next, referring to FIG. 5A or 5B, a lower passivation film 130 isattached to a lower part of the flexible substrate 112 after theflexible substrate 112 is separated from the supporting substrate.

The lower passivation film 130 may be disposed at both the display areaDA and the peripheral area PA.

Referring to FIG. 5A, FIG. 5B, or FIG. 6, a bottom side of the lowerpassivation film 130 may have protrusions and depressions including aplurality of grooves 135.

The plurality of grooves 135 may be regularly or irregularly disposed,and the grooves 135 may equally have regular or irregular shapes.

The grooves 135 may respectively have a triangular shape, as shown inFIG. 5A or 5B, or may respectively have a quadrangular shape, as shownin FIG. 6, such as a trapezoidal shape and the like.

An interval between the neighboring grooves 135 may be zero, as shown inFIG. 5A or 5B, or may be larger than zero, as shown in FIG. 6.

A distance between the grooves 135 and a top surface of the lowerpassivation film 130 may be from about 5 μm to about 50 μm, but it isnot limited thereto.

Moreover, the height of the grooves 135 of the lower passivation film130 may be from about 10 μm to about 100 μm, but it is not limitedthereto.

The lower passivation film 130 may include films such as polyethyleneterephthalate (PET) and the like, and the plurality of grooves 135 maybe formed by an imprinting method.

An adhesive layer (not illustrated) may be further disposed between thelower passivation film 130 and the flexible substrate 112.

The adhesive layer may include silicon, urethane, acryl, and the like,and may further include nanoparticles made of a silicon oxide SiO_(x),aluminum, and the like. The thickness of the adhesive layer may be fromabout 5 μm to about 50 μm, but it is not limited thereto.

When the lower passivation film 130 is attached to a bottom surface ofthe flexible substrate 112 and then the first peripheral area PA_a and apart of the second peripheral area PA_b disposed thereunder are benttowards a rear side of the display area along the bending line CL,stresses applied to the display element layer 200 may be reduced andbending may be easily performed.

Accordingly, the stress, which is a deforming force, applied to thedisplay element layer 200 may be reduced such that damage to the displayelement layer (e.g., the light emitting layer) 200 including the thinfilm transistor, the light emitting diode LD, the encapsulation layer379, the wiring portions WR1 and WR2, and the pad area PDA may bereduced.

FIG. 5A and FIG. 5B respectively illustrate a strain distribution graphG when the display panel manufactured by a manufacturing methodaccording to an exemplary embodiment of the present invention includesthe neutral plane balancing layer 380 and the lower passivation film130.

Based on the neutral plane NP, the upper part shows a tensile strain andthe lower part shows a compressive strain.

According to an exemplary embodiment of the present invention, theneutral plane NP of the strain distribution graph G may be disposedclose to the display element layer 200, as shown in FIG. 5A, or may bedisposed in the display element layer 200, as shown in FIG. 5B.

Further, depending on the thickness T1 of the neutral plane balancinglayer 380, the stress applied to the display element layer 200 may be acompressive stress.

Accordingly, when the first peripheral area PA_a and the part of thesecond peripheral area PA_b disposed thereunder are bent towards therear side of the display area DA along the bending line CL, a tensilestress applied to the display element layer 200 including the wiringportions WR1 and WR2 and the pad area PDA may be reduced or a lessdamaging stress may be applied to the display element layer 200, therebyresulting in preventing the display element layer 200 from being damagedand easier bending of the first peripheral area PA_a and the part of thesecond peripheral area PA_b disposed thereunder. Referring to FIG. 7,after the first peripheral area PA_a and the part of the secondperipheral area PA_b disposed thereunder in the display panel whichincludes the neutral plane balancing layer 380 and the lower passivationfilm 130 are bent towards the rear side of the display area DA along thebending line CL, the first peripheral area PA_a and the part of thesecond peripheral area PA_b disposed thereunder at respective lateralsides of the display area DA are not virtually seen when viewed from afrontal side of the display panel.

In this instance, the curvature radius of a part of the display panelfolded along the bending line may be from about 0.5 mm to about 10 mm.

Further, the entire flexible display panel may be bent with anapproximate curvature radius of about 50 mm to about 400 m to form acurved display panel.

Thus, when viewed from the frontal side of the display panel, only thedisplay area DA is seen, as shown in FIG. 8, while the peripheral areaPA at respective lateral sides of the display area disappears.

That is, non-display area of the flexible display panel, which does notdisplay an image, may be easily removed.

As described above, according to an exemplary embodiment of the presentinvention, attaching the lower passivation film 130 having the pluralityof grooves 135 to the bottom side of the flexible substrate 112 andforming the neutral plane balancing layer 380 at the upper part of thedisplay element layer 200 of the peripheral area PA may simultaneouslyresult in easier bending of the peripheral area PA and preventing thedisplay element layer 200 including the wiring portions WR1 and WR2 andthe pad area PDA from being damaged.

FIG. 9 is a top plan view illustrating the non-display area of thedisplay panel folded backward according to an exemplary embodiment ofthe present invention.

Referring to FIG. 9, a flexible display panel according to an exemplaryembodiment of the present invention is almost the same as the flexibledisplay panel according to the exemplary embodiment described above, buta bottom surface of the passivation film 130 attached to the lower partof the flexible substrate 112 may not have protrusions and depressions.

Although the lower part of the lower passivation film 130 does not haveprotrusions and depressions, since at least the neutral plane balancinglayer 380 overlapped with the bending line CL is still formed at theupper part of the display element layer 200 of the second peripheralarea PA_b, the neutral plane tensile stress applied to the displayelement layer 200 may be virtually reduced as the position of theneutral plane NP is disposed closer to the display element layer 200when the first peripheral area PA_a and the part of the secondperipheral area PA_b disposed thereunder are folded towards the rearside of the display area DA along the bending line CL.

Accordingly, the first peripheral area PA_a and the part of the secondperipheral area PA_b disposed thereunder may be easily bent, and thenon-display area may be easily removed from the display panel withoutdamaging the display element layer 200 including the wiring portions WR1and WR2 and the pad area PDA.

Now, together with the drawings described above, referring to FIG. 10 toFIG. 13, a manufacturing method of a flexible display panel and theflexible display panel manufactured thereby according to an exemplaryembodiment of the present invention will be described.

The same constituent elements as the exemplary embodiments describedabove designate the same reference numerals, and the repeateddescription will be omitted.

FIG. 10 is a top plan view of the display panel before the peripheralarea is folded backwards in a manufacturing process of a flexibledisplay panel according to an exemplary embodiment of the invention,FIG. 11 is a cross-sectional view of the display panel of FIG. 10 takenalong the line XI-XI, FIG. 12 is a cross-sectional view showing a statein which a part of the peripheral area of the display panel according toan exemplary embodiment of the present invention is folded forwards, andFIG. 13 is a cross-sectional view showing a state in which a part of thedisplay panel of FIG. 12 is folded backwards.

First, referring to FIG. 10 and FIG. 11, a flexible substrate 112 isformed on a supporting substrate (not illustrated) made of glass orplastic.

The flexible substrate 112 includes a display area DA displaying animage and a peripheral area PA outside of the display area DA.

The peripheral area PA includes a first peripheral area PA_a in whichthe wiring portions WR1 and WR2 are disposed, and a second peripheralarea in which a pad area is disposed.

Next, a barrier layer 111 may be formed on the flexible substrate 112.

The barrier layer 111 may be omitted.

Next, a display element layer 200 including a plurality of thin films isformed on the barrier layer 111.

The display element layer 200 includes a plurality of signal lines whichare disposed in the display area, and a plurality of pixels PX which areconnected thereto and are arranged in an approximate matrix form.

The signal line may include a plurality of scanning signal lines totransmit a scanning signal, and a plurality of data lines to transmit adata signal.

The display element layer 200 may include wiring portions WR1 and WR2which are disposed in the peripheral area PA, and a pad area PDA whichis connected to a driving portion (not illustrated) to drive pixel PX.

The pad area PDA and the wiring portions WR1 and WR2 may be connected toeach other, and may be made of a conductive material.

The wiring portions WR1 and WR2 may be connected to a plurality ofsignal lines of the display area DA, and may be disposed at respectivelateral sides of the display area DA.

The display element layer 200 may include a thin film transistor, alight emitting diode LD, and an encapsulation layer 379, and a detailedstructure of the display element layer 200 may be the same as that ofthe exemplary embodiment described above.

The wiring portions WR1 and WR2 and the pad area PDA of the peripheralarea PA are disposed on the same layer as a gate conductive layer ordata conductive layer, and may be integrally formed when the gateconductive layer or data conductive layer is formed.

Next, referring to FIG. 11, to improve visibility by reducing reflectionof external light, an anti-reflection layer 390 may be attached to anupper part of the display element layer 200 of the display area DA.

The anti-reflection layer 390 may be disposed only on the display areaDA, or may not only be disposed on the display area but may also furtherextend to intrude on the first peripheral area PA_a.

The anti-reflection layer 390 may include a polarizer (not illustrated)or a plurality of thin film layers (not illustrated).

In case the anti-reflection layer 390 includes the plurality of thinfilm layers, the plurality of thin film layers may include at least onethin metal film layer and at least one dielectric layer which arealternately laminated.

Next, the supporting substrate is separated from the flexible substrate112.

A lower passivation film 130 is attached to a bottom side of theflexible substrate 112 after separating the flexible substrate 112 fromthe supporting substrate.

The lower passivation film 139 may be disposed in both the display areaDA and the peripheral area PA.

Referring to FIG. 11, the bottom side of the lower passivation film 130may have protrusions and depressions including a plurality of grooves135.

The plurality of grooves 135 may be regularly or irregularly disposed,and the grooves 135 may have regular or irregular shapes.

Each groove 135 may have a triangular shape, as shown in FIG. 11, or mayhave a quadrangular shape such as trapezoidal shape and the like, asshown in FIG. 6 described above.

An interval between the grooves 135 and the top side of the lowerpassivation film 130 may be from about 5 μm m to about 50 μm, but it isnot limited thereto.

Moreover, the height of the grooves 135 of the passivation film 130 maybe from about 10 μm to about 100 μm, but it is not limited thereto.

The lower passivation film 130 may include films such as polyethyleneterephthalate (PET) and the like, and may be formed with the pluralityof grooves 135 by an imprinting method.

Next, referring to FIG. 10 to FIG. 12, the first second peripheral areaPA_a and an outer portion of the second peripheral area PA_b disposedthereunder in the display area including the lower passivation film 130are folded forward along a first bending line CL1.

The first bending line CL1 divides the first peripheral area PA_a intotwo areas, and the horizontal lengths D2 and D3 of the divided areas maybe the same as or different from each other.

Referring to FIG. 12, the first peripheral area PA_a folded forward, andthe part of the second peripheral area PA_b disposed thereunder does notintrude on the display area DA.

The curvature radius of the part folded along the first bending line CL1may be from about 0.5 mm to about 10 mm.

Referring to FIG. 12, the first peripheral area PA_a folded forwardalong the first bending line CL1, and the outer portion of the part ofthe second peripheral area PA_b thereunder may raise the neutral planeNP by the thickness T2.

That is, the outer portion of the peripheral area PA_a folded upwardsalong the first bending line CL1 may raise the position of the neutralplane NP such that a tensile stress applied to the display element layer200 may be reduced or a less damaging compressive stress may be appliedto the display element layer 200 when the peripheral area PA foldedalong the second bending line CL2 is later folded towards the rear sideof the display area DA.

Accordingly, the first peripheral area PA_a folded upwards along thefirst bending line CL1 and the outer portion of the part of the secondperipheral area PA_b disposed thereunder may perform the same functionas the neutral plane balancing layer 380 according to the exemplaryembodiment described above. The first bending of the display panel alongthe first bending line CL1 may place the neutral plane NP higher thanthe position from which the lower passivation film 130 and is 120 μmaway, but it is not limited thereto.

Next, referring to FIG. 10 and FIG. 13, the peripheral area PA foldedupwards along the first bending line CL1 is folded along the secondbending line CL2 towards the rear side of the display area DA such thatthe peripheral area PA disposed at respective lateral sides of thedisplay area DA is not virtually seen when viewed from the frontal sidethereof.

In this case, the curvature radius of a part of the display panel foldedalong the second bending line CL2 may be from about 0.5 mm to about 10mm.

Herein, the bending line CL2 may virtually overlap a border line betweenthe display area DA and the first peripheral area PA_a, or may bedisposed on the periphery of the border line.

According to an exemplary embodiment of the present invention, since alower surface of the lower passivation film 130 includes protrusions anddepressions formed with the plurality of grooves 135, stresses appliedto the display element layer 200 may be reduced and bending may beeasily performed when folding the display panel along the first andsecond bending lines CL1 and CL2.

Accordingly, a stress, which is a deformation force, applied to thedisplay element layer 200 may be reduced, and damage to the thin filmtransistor, the light emitting diode LD, the encapsulation layer 379,the wiring portions WR1 and WR2, the pad area PDA may be reduced.

Thus, as shown in FIG. 8 described above, when viewed from the frontalside of the display panel, only the display area DA is seen, and thefirst peripheral area PA_a and the second peripheral area PA_b disposedthereunder may disappear.

That is, the non-display area incapable of displaying an image may beeasily removed in the flexible display panel.

Thus, according to an exemplary embodiment of the present invention, thelower passivation film 130 formed with the plurality of grooves 135 isattached to the lower part of the flexible substrate 112, and theperipheral area PA is folded twice along the first and second bendinglines CL1 and CL2, thereby resulting in easier bending of the peripheralarea PA along the second bending line CL2 and simultaneously preventingthe display element layer 200 including the wiring portions WR1 and WR2and the pad area PDA from being damaged.

FIG. 14 is a cross-sectional view showing a condition in which a part ofthe peripheral area of the display panel according to an exemplaryembodiment of the present invention is folded forwards, and FIG. 15 is across-sectional view showing a condition in which a part of the displaypanel of FIG. 14 is folded backwards.

Referring to FIG. 14, a flexible display panel according to an exemplaryembodiment of the present invention is almost the same as the flexibledisplay panel according to the exemplary embodiment illustrated in FIG.10 to FIG. 13, but a bottom side of the passivation film 130 attached tothe lower part of the flexible substrate 112 may not have protrusionsand depressions.

Although the lower part of the lower passivation film 130 does not haveprotrusions and depressions, since the peripheral area is folded upwardsalong the first bending line CL1 and substantially raises the neutralplane NP, a tensile stress applied to the display element layer 200 maybe reduced or a compressive stress may be applied thereto when theperipheral area PA is folded towards the rear side of the display areaalong the second bending line CL2.

Accordingly, without damaging the display element layer 200, theperipheral area PA may be easily bent and the non-display area may beeasily removed from the display panel.

When a couple of the flexible display panels according to an exemplaryembodiment described above are connected together, an all-round displaydevice capable of displaying an image at both front and rear sides maybe embodied without a non-display area.

While this invention has been described in connection with variousembodiments thereof, it is to be understood that the invention is notlimited to the disclosed embodiments, but, on the contrary, is intendedto cover various modifications and equivalent arrangements includedwithin the spirit and scope of the appended claims.

Description of Symbols 111: barrier layer 112: flexible substrate 121:scanning signal line 124a, 124b: control electrode 130: lowerpassivation film 135: groove 140: gate insulation layer 154a, 154b:semiconductor 171: data line 172: driving voltage line 180a, 180b:passivation layer 183a, 183b, 184, 185a, 185b, 185c: contact hole 191:pixel electrode 270: common electrode 360: pixel definition layer 370:light emitting member 371, 375: organic common layer 373: light emittinglayer 379: encapsulation layer 380: neutral plane balancing layer 390:anti-reflection layer

What is claimed is:
 1. A flexible display panel comprising: a flexiblesubstrate including a first flat area, a second flat area, and a bendingarea between the first flat area and the second flat area; a wire overthe first flat area, the second flat area, and the bending area; apolarizer over the flexible substrate; a lower film under the flexiblesubstrate; and a first layer comprising a resin and being over theflexible substrate, wherein the bending area of the flexible substrateis bent along a first axis such that the first flat area and the secondflat area face each other, wherein the first layer overlaps the bendingarea in a first direction perpendicular to an upper surface of theflexible substrate, wherein a side surface of the first layer is incontact with a side surface of the polarizer, wherein the lower filmincludes at least one depression overlapping the bending area, andwherein the lower film overlaps the first flat area and the second flatarea.
 2. The flexible display panel of claim 1, wherein the at least onedepression overlaps the bending area.
 3. The flexible display panel ofclaim 2, wherein the depression has at least three sides that extend indifferent directions from each other in a sectional view.
 4. Theflexible display panel of claim 2, wherein the depression has at leastthree planes that extend in different directions from each other, and atleast two edges respectively located between two adjacent planes of theat least three planes.
 5. The flexible display panel of claim 1, furthercomprising a display element layer comprising: thin film transistors;and light emitting elements over the thin film transistors, wherein thedisplay element layer is between the flexible substrate and thepolarizer.
 6. The flexible display panel of claim 5, wherein the atleast one depression is configured to reduce stress applied to thedisplay element layer when the flexible substrate is bent.
 7. Theflexible display panel of claim 5, wherein the wire is at the displayelement layer.
 8. The flexible display panel of claim 1, furthercomprising: a barrier layer over the flexible substrate, the barrierlayer comprising an inorganic insulating material; and a display elementlayer comprising thin film transistors, and light emitting elements overthe thin film transistors, wherein the display element layer is betweenthe barrier layer and the polarizer.
 9. The flexible display panel ofclaim 8, wherein the barrier layer comprises an inorganic insulatingmaterial.
 10. The flexible display panel of claim 8, wherein the displayelement layer further comprises an encapsulation layer for encapsulatingthe light emitting elements.
 11. The flexible display panel of claim 1,wherein a thickness of the first layer is from about 10 μm to about 150μm.
 12. The flexible display panel of claim 1, wherein a thickness ofthe first layer in the first direction is less than a thickness of thepolarizer in the first direction.
 13. The flexible display panel ofclaim 1, further comprising a display element layer comprising: thinfilm transistors; and light emitting elements over the thin filmtransistors, wherein the polarizer and the first layer are at a samelevel on the display element layer.
 14. The flexible display panel ofclaim 1, further comprising a display element layer having an uppersurface, wherein the polarizer and the first layer contact the uppersurface of the display element layer.
 15. The flexible display panel ofclaim 1, wherein a curvature radius of the first layer is greater than acurvature radius of the wire over the bending area.